Learn me about on demand water heaters!

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Exmasonite

Feeling the Heat
Oct 3, 2010
321
Novi, MI
Hey everybody-

Wanted to pick the collective's brains about on demand water heater. Purchased a house in the fall, it's a 23 y/o log cabin with a fuel oil boiler and 2 zone radiator (1st and 2nd floor, about 1500 sq ft on 1st floor, 1000 sq ft on 2nd). Boiler also produces hot water for the house- 3 full bath, washer, etc. Family size is 2 (me and the wife) and likely to be that way for 5-7 yrs if not forever.

The water "tank" is about 20 yrs old. Not sure what the life span on one of those suckers is... i figure it doesn't do much other than hold water and maybe monitors temp to kick boiler on when water cools.

Like everybody else here, i'm trying to decrease my dependence on the oil man. Wondering if somebody could fill me in on pros/cons of an on demand water heater. I think there's room on the electrical panel for it so that shouldn't be an issue.
 
Most, the huge majority, are fueled by NG or propane. They take a lot of eneergy to raise water from say 50 to 120. So much energy that an electrical powered heater requires a huge circuit. You may be better off with an electric tank heater if you don't have gas available. Or you could use this as an excuse to get that gas range you've always wanted.
 
highbeam-

Thanks for the info... still starting the research on that and first sight i came to mentioned electrical.

I do have access to propane in the house... generator, range, and fireplace all run on it. Of course, tanks/propane appliances are on the exact opposite side of house from water entry/utility room.

How "close" do such appliances have to be to the destination? Do people have 1 big one in the basement or multiple smaller units closer to the shower, etc. ?
 
It sounds like you have an indirect water heater, which should give you what you want from an on demand heater... efficiency, lots of HW, longevity. They supposedly have very little stand by losses due to their insulation. Many also have a stainless inner tank so 20 years isn't necessarily at the end of their life.

When my electric water heater goes I'll be installing an indirect WH.

Matt
 
We are building a house right now and my research of on demand water heaters brought up two important negatives.
One is that the pay back is somewhere in the neighborhood of 20 years and the other is that if you are on a well, as we are, that you will have problems with mineral build up. One source said that you have to run a gallon of vinegar through
them once a month if you have hard water and even with that their useable life will be shortened. We decided to go
with a standard electric hot water heater with an add on insulation blanket. We are also looking at plans to later add
an inexpensive home made passive hot water heater to supplement. You can find plans for this by doing a search on
Yahoo and also check You Tube. Hope this helps.
Jbird
 
I've been using a bosh aquastar for the past 5 years. Model 125 with standing pilot.

I'm on a well and have no problems with mineral buildup though my water doesn't seem to be particularly high in mineral content either. I definitely use less propane than I did with a standard heater, but I can't say how significant exactly since I just see the reflection in greater time between refills.

My pressure tank is set at 30/50 and my well water is teeth-shattering cold this time of year, and slightly warmer in the Summer months.

The delivery line to the bathroom sink is 76" long and it takes about 12 seconds for the water at the tap to arrive at max temp -less time of course for warm water.(winter water temp.)

Delivery line to the kitchen sink is 284" and it takes a bit over 30 seconds for the water at the tap to arrive at max temp. A bit more in the am when the water in the heater lines is cold.

With well insulated lines and use of hot water throughout the day the arrival time for hot water is much less.

The 125 will supply the kitchen and bath sinks simultaneously with hot water (2 minor appliances), but if you're taking a shower and someone opens a hot faucet you'll get an ice cold blast. It's good for 1 major appliance. There's bigger units that will supply a higher demand.

On a well with lower pressure than municipal water you need to open the faucet enough to turn the heater on. In other words, the level of pressure running through the lines is what controls how intense the flames will be. High flow, high flames to adequately heat the water. Low flow/low flames so you won't scald yourself.
Now, the problem I see on our system is that if you want a very low flow of water to just rinse the dishes or your hands and your pressure is at the low end, the heater won't come on with just that very low flow. When the tank is at the high end you can turn on the heater with a semi low flow, but go too low and it won't come on anyhow. My kitchen is right next to the bathroom where the heater is so I can hear it ignite. But there are times when you might not be paying attention, or someone not familiar is using the hot water and the heater goes off or doesn't come on because the flow is too low and you're standing around for a half a minute or more once you realize you've lost the hot water while you wait for the hot water to cycle through the lines. With a standing hot water tank you can use any level of flow. If you're on municipal water I believe the high pressure will mostly eliminate this problem. I haven't tried upping my pressure to 40/60, but I'm sure it would help. When I was at 20/40 it was much worse.

I love the constant supply of hot water and the fact that I'm not heating water all day when nobody's home or if we go away for a weekend. It's taken some getting used to, but I'm satisfied. Not sure if I'll be putting one in the new house we'll be starting soon since I'd like to preheat my water with my stove in the Winter and the sun in the Summer. Unless they have new models with temperature sensors, introducing preheated water to the tank would result in excessively overheated water
 
eatenbylimestone-

Thanks for the info. I guess that's an accurate description of the system. Just worried that we're still going through a lot of oil and was blaming the hot water since wood heat does the majority of the house now. We've gone through about 150 gallons since 12/20/10 and i am still trying to figure out if that is good or bad. The warmer weather should really help me figure out how much fuel oil the hot water is costing me once i don't have the cool weather/home heating to confound the issue.
 
We have the aquastar 240 ng model, it replaced a tank heater that was about 30 years old. the gas lines had to be 3/4'' so some had to be replaced to do the install. overall its the same for delivering hot water to the furthest point which is basement to top floor in 30 seconds. we have taken showers when the dishwasher was running or the washing machine was on and or sinks or toilets used. it slows down the flow rate we dont run 2 major at the same time if we can help it. the thing i like is that if you ever need a ton of long lasting hot water you have it. seems when i am rinsing a few dishes in the sink or scrubbing a large pot if the level is low the water goes cold as mentioned . that is the only thing to get used to, it doesnt bother me simply because id lived with one before and this is just how they operate. i definately like the water on demand as we arent big hot water users and it doesnt make sense to keep a tank on demand for our usage. i can answer more questions if need be. pete
 
http://www.revisionenergy.com/solar-hot-water-solar-power.php

Take a peak at solar
With this system we just installed
All of spring summer fall hot water should
Be powered by that gigantic nuclear fusion
Power plant in the sky
Even in winter a good junk of hot water
Is preheated

Between this solar hot water system and my
Wood burning insert,I hope not to hear the oil burner for
Nearly as much

$1000 state (ME)
$3000 fed
Means close to 40% is subsidized
More in new Hampshire
 
dvellone said:
I've been using a bosh aquastar for the past 5 years. Model 125 with standing pilot.

I'm on a well and have no problems with mineral buildup though my water doesn't seem to be particularly high in mineral content either. I definitely use less propane than I did with a standard heater, but I can't say how significant exactly since I just see the reflection in greater time between refills.

My pressure tank is set at 30/50 and my well water is teeth-shattering cold this time of year, and slightly warmer in the Summer months.

The delivery line to the bathroom sink is 76" long and it takes about 12 seconds for the water at the tap to arrive at max temp -less time of course for warm water.(winter water temp.)

Delivery line to the kitchen sink is 284" and it takes a bit over 30 seconds for the water at the tap to arrive at max temp. A bit more in the am when the water in the heater lines is cold.

With well insulated lines and use of hot water throughout the day the arrival time for hot water is much less.

The 125 will supply the kitchen and bath sinks simultaneously with hot water (2 minor appliances), but if you're taking a shower and someone opens a hot faucet you'll get an ice cold blast. It's good for 1 major appliance. There's bigger units that will supply a higher demand.

On a well with lower pressure than municipal water you need to open the faucet enough to turn the heater on. In other words, the level of pressure running through the lines is what controls how intense the flames will be. High flow, high flames to adequately heat the water. Low flow/low flames so you won't scald yourself.
Now, the problem I see on our system is that if you want a very low flow of water to just rinse the dishes or your hands and your pressure is at the low end, the heater won't come on with just that very low flow. When the tank is at the high end you can turn on the heater with a semi low flow, but go too low and it won't come on anyhow. My kitchen is right next to the bathroom where the heater is so I can hear it ignite. But there are times when you might not be paying attention, or someone not familiar is using the hot water and the heater goes off or doesn't come on because the flow is too low and you're standing around for a half a minute or more once you realize you've lost the hot water while you wait for the hot water to cycle through the lines. With a standing hot water tank you can use any level of flow. If you're on municipal water I believe the high pressure will mostly eliminate this problem. I haven't tried upping my pressure to 40/60, but I'm sure it would help. When I was at 20/40 it was much worse.

I love the constant supply of hot water and the fact that I'm not heating water all day when nobody's home or if we go away for a weekend. It's taken some getting used to, but I'm satisfied. Not sure if I'll be putting one in the new house we'll be starting soon since I'd like to preheat my water with my stove in the Winter and the sun in the Summer. Unless they have new models with temperature sensors, introducing preheated water to the tank would result in excessively overheated water

I believe that some models do have temp sensors so that you can use preheated water without overheating. They cost a little more.
 
I have a Bosch Aquastar. Not sure of the model. It's about 10 years old -- one that works for a single appliance.

It's great for unlimited hot water, and there's no tank to go bad.

A problem arises if you use it for doing dishes by hand if you like to turn the water on and off, because every time you turn the water off (or slow) the heater cuts off (keeps it from exploding). When you turn it back on, it takes a moment for it to sense the water flowing and to light the burner. During this period (a few seconds) cold water flows into the pipes, where it mixes with the hot that's there.

I don't think it really saves any gas either. It would if you only used it on weekends or something, but if you use hot water a few times a day, then every time you turn on the tap you've got a 250,000 BTU burner running.

If I had room in my house, I'd definitely install a tank LP water heater instead of a tankless.
 
Indirect water heaters are not very efficient if you're not using the boiler as a primary heat source. Firing my boiler solely to run the indirect was costing me about $100/month in oil. I've since switched to an electric heat pump water heater which is about $25/month to run. Mine has a 2.35EF (about 2.5X more efficient than a standard electric WH). Solar HW is great too, I'd like to install a closed-loop system someday to tie in with my water heater, but too much $$$ right now.
 
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